1. Field of the Invention
The present invention relates to ultrasonic diagnostic probes and more particularly to a ultrasonic diagnostic probe in which the orientation of a piezoelectric vibrator provided in a shaft is variable.
Recently, ultrasonic diagnosis is extensively used in scanning the body cavity of a human body as well as in scanning the surface of a human body. Ultrasonic scanning in the body cavity provides more detailed information regarding the region diagnosed.
A problem with the scanning of the body cavity is that the pattern of ultrasono-tomographic images is limited because a probe is mounted at the end of a shaft.
2. Description of Prior Art
Nowadays, ultrasono-tomographic diagnosis is extensively practiced by doctors. In the field of ultrasonic diagnosis of the heart, there is known a method called transesophagus echo probe of the heart in which an ultrasonic diagnostic probe is inserted via an mouth and an esophagus for diagnosis of the heart.
A description of a conventional ultrasonic diagnostic probe will be given, with reference to FIGS. 1, 2, 3A, 3B, 3C, 4A, 4B, 4C and 5, using esophagus echo probe of the heart as an example.
FIG. 1 shows the construction of a conventional ultrasonic diagnostic probe 1. The ultrasonic diagnostic probe 1 comprises a tube-like shaft 2 and array piezoelectric vibrators 3a and 3b provided at right angles to each other near the end of the shaft 2. It is known that the transmission and reception of ultrasonic waves by the array piezoelectric vibrators 3a and 3b occur in specific directions. In the construction of FIG. 1 where the two array piezoelectric vibrators are secured in place at right angles to each other, images of only two ultrasono-tomographic sections 4a and 4b can be obtained, the sections 4a and 4b being at right angles to each other.
In order to resolve the above-described disadvantage of the ultrasonic diagnostic probe 1 of FIG. 1 and to enable images of more ultrasono-tomographic sections to be obtained, an ultrasonic diagnostic probe 6 shown in FIG. 2 has been proposed. The ultrasonic diagnostic probe 6 is configured such that an array piezoelectric vibrator 5 is made to rotate. As shown in FIGS. 3A, 3B and 3C, according to the ultrasonic diagnostic probe 6, a section 7 whose image is obtained is made to rotate in response to the rotation of the piezoelectric vibrator 5. Hence, more images can be obtained using the ultrasonic diagnostic probe 6 than using the conventional ultrasonic diagnostic probe 1.
However, the section 7 whose image can be obtained using the construction of the ultrasonic diagnostic probe 6 is always at right angles with respect to the length of the shaft 2, that is, with respect to the direction A indicated by an arrow in FIG. 4A.
Therefore, as shown in FIGS. 4B and 4C, the end of the ultrasonic diagnostic probe 6 should be moved in order to obtain a section that is not perpendicular to the shaft 2. FIG. 4B indicates that a desired section 7 is inclined by an angle +.theta..sub.1 to the perpendicular line, and FIG. 4C indicates that a desired section 7 is inclined by an angle +.theta..sub.1 to the perpendicular line.
When the piezoelectric vibrator 5 is separated from a wall of an esophagus 8 in which the ultrasonic diagnostic probe 6 is inserted, the propagation characteristic of ultrasonic wave worsens. Therefore, it is necessary to operate the ultrasonic diagnostic probe 6 so that its end is not removed from the inner wall of the esophagus 8. Thus, a problem with the ultrasonic diagnostic probe 6 is that a skill of a doctor is required in order to prevent the end of the piezoelectric vibrator 5 from being removed from the inner wall 8 of the esophagus.
When one needs an image of a section resulting from rotating (clockwise or counterclockwise) the ultrasonic diagnostic probe 6 away from its position shown to the left in FIG. 5 around the central axis of the esophagus 8 by a predetermined angle (for example, .theta..sub.2), the shaft 2 should be rotated by an angle .theta..sub.2, as shown to the right in FIG. 5 to obtain the required section. The operation of the ultrasonic diagnostic probe 6 is difficult in this respect, too.